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Table 3 Prevalence of correct answers in the intervention ("Int.") and control ("Con.") group, and prevalence ratio of correct answers between the groups, for all respondents and by educational attainment

From: Communicating population health statistics through graphs: a randomised controlled trial of graph design interventions

  All respondents Non university-qualified* University-qualified*
Interventions and interpretation tasks Int. % (n= 176) Con. % (n= 187) Ratio (95% CI) Int. % (n= 56) Con. % (n= 57) Ratio (95% CI) Int. % (n= 116) Con. % (n= 124) Ratio (95% CI)
Interventions: 1. Simplified series labels; 2. Footnote explaining age standardisation (see Figure 1)
Understand the meaning of a point reading of an incidence rate 80.7 57.2 1.4 (1.2–1.6) 76.8 45.6 1.7 (1.2–2.3) 81.9 62.9 1.3 (1.1–1.5)
Understand the influence of age standardisation on comparisons between incidence rates 58.0 36.9 1.6 (1.3–2.0) 42.9 22.8 1.9 (1.1–3.3) 65.5 44.4 1.5 (1.2–1.9)
Interventions: 1. Removed one category from a stacked layer graph; 2. Footnote explaining how to interpret the thickness of a layer (see Figure 2)
For a single disorder, estimate the difference between incidence rates between two age points 57.4 57.8 1.0 (0.8–1.2) 51.8 47.4 1.1 (0.8–1.6) 60.3 63.7 0.9 (0.8–1.2)
Compare an incidence rate reading for a disorder by sex across adjacent graphs 85.2 88.2 1.0 (0.9–1.1) 83.9 82.5 1.0 (0.9–1.2) 87.1 90.3 1.0 (0.9–1.1)
Describe the trend by age along a layer in the graph 69.9 84.0 0.8 (0.7–0.9) 58.9 80.7 0.7 (0.6–0.9) 75.0 86.3 0.9 (0.8 – 1.0)
Broad comparison of the total rate (sum of all layers) within an age range by sex across adjacent graphs 89.2 85.6 1.0 (1.0–1.1) 89.3 87.7 1.0 (0.9–1.2) 90.5 83.9 1.1 (1.0–1.2)
Interventions: 1. Changed a divided bar graph to a side-by-side divided bar graph; 2. Footnote explaining acronyms used in the graph (see Figure 3)
Compare the magnitude of YLL and YLD for a single disease category and sex 65.9 74.9 0.9 (0.8–1.0) 69.6 71.9 1.0 (0.8–1.2) 64.7 77.4 0.8 (0.7–1.0)
Know that YLD represents disability burden and select the disease with the highest value for a single sex 32.4 12.8 2.5 (1.6–3.8) 33.9 10.5 3.2 (1.4–7.5) 31.9 14.5 2.2 (1.3–3.6)
For a single disease, compare the magnitude of YLLs by sex 85.8 88.8 1.0 (0.9–1.1) 83.9 89.5 0.9 (0.8–1.1) 87.9 88.7 1.0 (0.9–1.1)
Select the disease with the highest number of DALYs for a single sex 83.0 67.9 1.2 (1.1–1.4) 80.4 61.4 1.3 (1.0–1.7) 85.3 71.8 1.2 (1.0–1.4)
Intervention: Removed one of three independent variables from the graph so that bars became undivided and there was no need for a legend (see Figure 4)
Read the total rate of YLL for a single geographic category and sex 93.8 80.2 1.2 (1.1–1.3) 89.3 71.9 1.2 (1.0–1.5) 96.6 83.9 1.2 (1.1–1.3)
Broad comparison of the magnitude of YLL rates between two geographic categories, regardless of sex 94.9 90.4 1.1 (1.0–1.1) 94.6 84.2 1.1 (1.0–1.3) 95.7 94.4 1.0 (1.0–1.1)
Broad comparison of the magnitude of YLL rates between sexes, regardless of geographic category 92.6 92.5 1.0 (0.9–1.1) 89.3 84.2 1.1 (0.9–1.2) 94.8 96.0 1.0 (1.0–1.1)
Intervention: Changed a population pyramid to a line graph (see Figure 5)
Broad comparison by sex of the overall population count across a range of age groups, for one geographic area 90.3 78.1 1.2 (1.1–1.3) 85.7 77.2 1.1 (0.9–1.3) 93.1 78.2 1.2 (1.1–1.3)
Broad comparison by geographic region across adjacent graphs of the total population size, regardless of age or sex 78.4 41.2 1.9 (1.6–2.3) 73.2 29.8 2.5 (1.6–3.8) 81.9 46.8 1.8 (1.4–2.2)
Broad comparison of the population size of younger and older segments of the population regardless of region 89.2 85.6 1.0 (1.0–1.1) 83.9 80.7 1.0 (0.9–1.2) 92.2 87.9 1.1 (1.0–1.1)
Interventions: 1. Changed a dot graph with confidence intervals ('hi-lo-close') graph to a bar graph; 2. Footnote providing a simple practical description of confidence intervals (see Figure 6)
Interpret the statistical significance of the difference between two countries of birth in the proportion of premature births 54.5 31.6 1.7 (1.4–2.2) 39.3 15.8 2.5 (1.3–4.9) 62.9 40.3 1.6 (1.2–2.0)
Compare the relative magnitude of the proportion of premature births between two countries of birth represented by adjacent graph bars 91.5 84.5 1.1 (1.0–1.2) 92.9 71.9 1.3 (1.1–1.5) 91.4 90.3 1.0 (0.9–1.1)
Compare the relative magnitude of the proportion of premature births between two countries of birth represented by more distant graph bars 79.5 50.3 1.6 (1.4–1.9) 80.4 35.1 2.3 (1.6–3.3) 80.2 58.1 1.4 (1.2–1.7)
Interventions: 1. Changed the title to a plain question that reflected the intepretation of the graph; 2. Changed some numeric y axis labels to descriptive explanations relating to the title; 3: Removed the footnote that had become redundant (see Figure 7)
Broad judgement of whether Aboriginal people had a higher risk of death than Australians overall 82.4 58.8 1.4 (1.2–1.6) 69.6 38.6 1.8 (1.3–2.6) 90.5 69.4 1.3 (1.2–1.5)
For one age group and sex, read the point estimate of the rate ratio 83.0 55.6 1.5 (1.3–1.7) 69.6 36.8 1.9 (1.3–2.8) 91.4 65.3 1.4 (1.2–1.6)
Understand the meaning of a death rate ratio for one age group and sex 84.7 59.9 1.4 (1.2–1.6) 71.4 42.1 1.7 (1.2–2.4) 92.2 69.4 1.3 (1.2–1.5)
Intervention: Reversed the scale of the vertical axis to represent increasing risk in the upward direction (see Figure 8)
Judge the relative magnitude of risk between the sexes in a single year 79.5 48.7 1.6 (1.4–1.9) 66.1 31.6 2.1 (1.4–3.2) 87.1 58.1 1.5 (1.3–1.8)
For one sex, judge the direction of the trend over time 60.2 20.9 2.9 (2.1–9.9) 62.5 19.3 3.2 (1.8–5.7) 58.6 21.8 2.7 (1.9–3.9)
Read the point estimate of risk for a single sex in a single year 90.9 85.6 1.1 (1.0–1.1) 78.6 77.2 1.0 (1.0–1.4) 97.4 91.1 1.1 (0.9–1.1)
Interventions: 1. Made the y axis ranges on two adjacent graphs match; 2. Slight simplification to the graph title (see Figure 9)
Broad judgment by virus across adjacent graphs of the relative difference in prevalence between the two subgroups 90.9 45.5 2.0 (1.7–2.4) 89.3 35.1 2.5 (1.8–3.7) 93.1 51.6 1.8 (1.5–2.2)
Broad judgement of which subgroup had a lower prevalence of HCV infection 80.7 75.9 1.1 (1.0–1.2) 78.6 66.7 1.2 (1.0–1.5) 81.9 79.8 1.0 (0.9–1.2)
Broad comparison by virus across the two graphs of the prevalence of infection in a single year, regardless of subgroup 92.0 63.6 1.5 (1.3–1.6) 87.5 47.4 1.9 (1.4–2.5) 94.8 73.4 1.3 (1.2–1.5)
Point reading of prevalence of HCV infection for a single year and subgroup 71.0 73.3 1.0 (0.9–1.1) 64.3 63.2 1.0 (0.8–1.3) 74.1 78.2 1.0 (0.8–1.1)
Intervention: Changed the graph type from a vertical bar graph to a line graph (see Figure 10)
Point reading of the proportion of deaths caused by a disease in a single year 83.0 82.9 1.0 (0.9–1.1) 78.6 73.7 1.1 (0.9–1.3) 86.2 88.7 1.0 (0.9–1.1)
Judge which disease had the lowest proportion of deaths in a single year 96.6 94.1 1.0 (1.0–1.1) 96.4 87.7 1.1 (1.0–1.2) 97.4 97.6 1.0 (1.0–1.0)
Judge which disease had the most increasing trend in the proportion of deaths over the period shown 83.5 76.5 1.1 (1.0–1.2) 75.0 56.1 1.3 (1.0–1.8) 89.7 85.5 1.1 (1.0–1.2)
Intervention: Changed a dot graph to a bar graph (see Figure 11)
Judge which sex had the greater proportion for a single injury category 93.8 89.3 1.1 (1.0–1.1) 92.9 78.9 1.2 (1.0–1.4) 94.8 95.2 1.0 (0.9–1.1)
Judge which injury category had the greatest proportion of hospital separations within a single sex 96.0 94.1 1.0 (1.0–1.1) 94.6 89.5 1.1 (1.0–1.2) 97.4 97.6 1.0 (1.0–1.0)
Intervention: Changed the graph type from a pie chart to a horizontal bar graph (see Figure 12)
Identify the category accounting for the largest proportion of cancers in a single sex 97.7 96.8 1.0 (1.0–1.1) 96.4 93.0 1.0 (1.0–1.1) 99.1 100.0 1.0 (1.0–1.0)
Identify the larger of two categories for a single sex 96.6 95.2 1.0 (1.0–1.1) 94.6 93.0 1.0 (1.0–1.1) 98.3 97.6 1.0 (1.0–1.1)
Comparison by sex across adjacent graphs of the contribution of one cancer to all cancers in each sex 95.5 63.6 1.5 (1.3–1.7) 92.9 80.7 1.2 (1.0–1.3) 97.4 56.5 1.7 (1.5–2.0)
Identify the cancer accounting for the smallest proportion of all cancers in a single sex 96.6 90.9 1.1 (1.0–1.1) 94.6 91.2 1.0 (0.9–1.2) 98.3 91.9 1.1 (1.0–1.1)
Point reading of the proportion of all cancers contributed by a single cancer for a single sex 92.0 25.7 3.6 (2.8–4.6) 91.1 40.4 2.3 (1.6–3.1) 93.1 19.4 4.8 (3.4–6.9)
  1. Con., control; DALY, disability-adjusted life year; HCV, hepatitis C virus; Int., intervention; YLD; years of living with a disease; YLL, years of life lost.
  2. *The number of university and non university-qualified participants does not add to the number of all respondents because 2% of intervention participants and 3% of control participants did not report their educational attainment.